Vinyl chloride-propylene copolymer resins which are presently produced are relatively non-porous, having irreversible plasticizer takeup numbers (ASTM D3367) of 10-16%. Vinyl chloride-propylene resin having such a relatively low porosity was acceptable for uses such as battery casings and phonograph records. In addition, there were not any rigorous residual monomer requirements in effect until recently.
However, the use of vinyl chloride-propylene resins for making video disks requires high porosity resins. Furthermore, residual monomer requirements for government regulatory compliance, as well as for a non-restricted application of the product, are much more stringent than in the past. Therefore, a suspension system capable of producing relatively porous vinyl chloride-propylene resins is desirable.
U.S. Pat. No. 3,592,800 discloses the suspension polymerization of vinyl chloride in the presence of a conventional high molecular weight protective colloid, such as hydroxypropylmethyl cellulose, and a low molecular weight polyvinyl alcohol which is 66-98 mole % hydrolyzed. The polymer product is said to have improved absorption of plasticizer.
U.S. Pat. No. 3,957,744 discloses in Comparative Example E the polymerization of vinyl chloride in the presence of a hydroxypropylmethyl cellulose and a polyvinyl acetate which is 75 mole % saponified. The disclosure is directed to the suppression of reactor wall fouling.
U.S. Pat. No. 4,143,224 discloses a process for making vinyl chloride polymers, which have a high plasticizer uptake, in the presence of a mixture of suspending agents comprising (a) a partially acetylated polyvinyl alcohol having 5 to 20 wt.% acetate units, (b) a cellulosic material, and (c) a partially acetylated polyvinyl alcohol having 31 to 35 wt.% acetate units. Comparative Examples A and C disclose a binary suspending system for the homopolymerization of vinyl chloride comprising a hydroxypropylmethyl cellulose and a polyvinyl alcohol containing 22 wt.% acetate groups and 33 wt.% acetate groups, respectively.
U.S. Pat. No. 4,258,163 describes the polymerization of vinyl chloride using as a suspending system a known protective colloid such as hydroxymethyl cellulose and a particular partially saponified polyvinyl acetate with a degree of hydrolysis of 30 to 65 mole %.
U.S. Pat. No. 4,283,516 discloses the suspension polymerization of vinyl chloride using a polyvinyl alcohol having a hydrolysis level of 68 to 78% together with a hydroxypropyl cellulose. The suspension grade polyvinyl chloride resin is claimed to possess both high bulk density and excellent porosity.
Although several of the above references suggest that other vinyl comonomers may be present in the polymerization recipe, there are no examples showing the copolymerization of vinyl chloride and propylene.
Other patents which show binary suspending systems include U.S. Pat. Nos. 3,340,243; 3,701,742; 3,917,548; 3,945,958 and 4,000,355. U.S. Pat. No. 3,945,958 discloses in Example 7 the copolymerization of vinyl chloride and propylene in the presence of a methyl cellulose and either a hydroxypropyl cellulose or a hydroxypropylmethyl cellulose.
U.S. Pat. Nos. 3,468,858 and 3,838,138 teach the suspension copolymerization of vinyl chloride and propylene.